Services and (Ibuidling material provided together with services) provided in the course of construction of a zero-rated building are zero-rated. You need to be sure that the various conditions are met eg this was a complete demolition and no retention of walls etc.
Look at the VAT notice on Building and Construction for details: https://www.gov.uk/guidance/buildings-and-construction-vat-notice-708
If you charge the wrong rate and say zero rate and HMRC says its 20% you fork the difference to HMRC hence its important to cover yourself through a contact/ contacting HMRC or ask client to get a VAT expert to provide written advice etc.